Frequency stabilized electrical musical instrument



Aug. 12, 1941. R' 2,252,189

FREQUENCY STABILIZED ELECTRICAL MUSICAL INSTRUMENT Filed Oct. 16, 1939 3 Sheets-Sheet l INVENTORV Aug. 12, 1941. N. LANGER FREQUENCY STABILIZED ELECTRICAL M USICAL INSTRUMENT Filed' Oct; 16, 1939 3 Sheets-Sheet 2 INVENTOR Aug. 12, 1941.

N. LANGER FREQUENCY STABILIZED ELECTRICAL MUSICAL INSTRUMENT Filed Oct. 16, 1939, 3 Sheets-Sheet 5 1 TL T INVENTOR Patented Aug. 12, 1941 FREQUENCY STABILIZED ELECTRICAL MUSICAL INSTRUMENT Nicholas Langer, New York, N. Y., assignor of sixty-six and two-thirds per cent to John Halmagyi, New York, N. Y.

Application October 16, 1939, Serial No. 299,619

16 Claims.

The present invention relates to electrical musical instruments of the type in which glowdischarge tube oscillators are employed for producing electrical oscillations of musical frequencies, and, more particularly, to an electrical musical instrument of the described character having great frequency stability.

As those skilled in the art know, electrical musical instruments of the glow-discharge tube type are capable of producing musical sounds of excellent musical quality in an extremely simple and economical manner. Although the frequency stability of glow-discharge tube oscillators is fair, difficulties were experienced on an industrial scale where it was desirable to maintain the proper frequency relationship of a large number of glow-discharge tube oscillators for a long time. It was already suggested to stabilize the frequency relationship of musical instruments of this type by providing a plurality of sources of constant frequency, such as tuning fork oscillators, and to impress an alternating voltage, or stabilizing voltage, of constant frequency derived from such sources on the glow-discharge tube oscillators having frequencies in a simple numerical relationship with thefrequency of the stabilizing voltage. This impression of a stabilizing voltage was accomplished by means of suitable coupling means of capacitive, inductive, or galvanic character. Thus, good results were obtained by providing an external electrode on the glow-discharge tube and to impress the stabilizing voltage upon the glow-discharge tube oscillator by means of this external electrode. Generally speaking, it was customary to provide twelve stabilizing oscillators, for example tuning fork oscillators, one for each note of the tempered scale; C, Ct, D, Dt, E, F, Ft, G, Gt, A, At, B, and to employ each of these stable oscillators for stabilizing all oscillators tuned to notes having the same name. In other words, in an electrical musical instrument having the range of seven octaves, the tuning fork oscillator tuned to C had to stabilize all of the various octaves of C, that is, seven oscillators. Likewise, the tuning fork oscillator tuned to the note D had to stabilize all of the seven oscillators corresponding to the octaves of D, etc. Examples of this system of stabilizing are disclosed in the U. S. Patents Nos. 2,017,542 and 2,044,360 to Langer.

Experience has demonstrated that while this system of stabilizing a large number of glowdischarge tube oscillators was generally satisfactory, the stabilizing effect decreased with the increase of the difference between the frequency of the stabilizing and of the stabilized oscillations. For example, a tuning fork oscillator having a frequency of 256 provided perfect and positive stabilization of glow-discharge tube oscillators having frequencies of 128, 256 and 512, but the stabilizing effect was considerably weaker for the oscillators having frequencies of 64 and 1024 and was rather weak for the frequencies of 32 and 2048 so that these oscillators had to be retuned from time to time. Of course, this circumstance caused great difliculties in producing electrical musical instruments of the glowdischarge tube type which would maintain their perfect tuning indefinitely and which in normal operation would not require any retuning at all.

I have discovered a simple and completely satisfactory solution of the outstanding problem.

It is an object of the present invention to provide an electrical musical instrument which eliminates the disadvantages and inconveniences of conventional electrical musical instruments.

It is another object of the present invention to provide an electrical musical instrument of the glow-discharge tube type having extremely high frequency stability and adapted to retain its correct and accurate tuning indefinitely.

A further object of the invention is to provide an electrical musical instrument having a large number of glow-discharge tube oscillators incorporated therein all of which are continuously producing electrical oscillations of various musical frequencies, the oscillators having frequencies in a simple numerical relationship to each other being interlocked by transferring energy from some of the oscillators to the others by means of suitable coupling means including external electrodes.

The invention also contemplates deriving a stabilizing frequency from a glow-discharge tube oscillator and impressing such stabilizing frequency upon one or more similar oscillators having a frequency which is a multiple or a submultipleof the frequency of such oscillator.

Still another object of the invention is to provide. a novel coupling and keying circuit for an electrical musical instrument embodying a plurality of continuously oscillating glow-discharge tube oscillators for selectively transferring oscillations from such oscillators onto a sound producing means in accordance with. the keys actuated.

It is also within contemplation of the invention to provide an electrical musical instrument of the glow-discharge tube typewhich is extremely simple in character, which will retain its tuning indefinitely, and which may be manufactured and sold on a practical and commercial scale at a low cost.

Other and further objects and advantages of the invention will become apparent from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 illustrates a circuit diagram of a pair of glow-discharge tube oscillators interlocked by means of an external electrode;

Fig. 2 depicts a similar circuit including three glow-discharge tube oscillators which are mutually interlocked by means of external electrodes;

Fig. 3 shows a circuit diagram having five glow-discharge tube oscillators incorporated therein tuned to frequencies which are in a simple numerical relationship to each other, such frequency relationship being stabilized between the various oscillators by means of external electrodes, while the absolute pitch of the complete system being adjustable by a tuning means in common for such oscillators;

Fig. 4 is a circuit diagram of an electrical musical instrument having stabilized glow-discharge tube oscillators incorporated therein and having coupling and keying means operatively associated therewith for the selective transfer of oscillations of stabilized frequency to a sound producing means in common for said oscillators;

Fig. 5 illustrates a circuit diagram of an electrical musical instrument similar to the one shown in Fig. 4, with the difference, however, that both stabilization of the relative frequencies of a plurality of glow-discharge tube oscillators as stabilization of the absolute frequencies of such oscillators are provided for;

Fig. 6 depicts a perspective view of a glow-discharge tube of preferred construction having an external electrode provided thereon;

Fig. 7 shows a similar view of a glow-discharge tube having a pair of annular external electrodes;

Fig. 8 is a circuit diagram which is a modification of the fundamental circuit shown in Fig. l; and

Fig. 9 is a circuit diagram of a pair of glowdischarge tube oscillators interlocked in accordance with the principles of the present invention in which the interlocking efiect may be adjusted.

Broadly stated, in accordance with the principles of the present invention, a plurality of glow-discharge tube oscillators are provided which by suitable selection of their constants (resistance, and capacity), are tuned to such frequencies which are in a simple numerical relationship to each other. Thus, it is generally preferred to tune such oscillators to successive octaves of a musical note. For example, when the oscillator of the lowest frequency produces an electrical oscillation of the frequency f, the subsequent oscillators are preferably tuned to frequencies corresponding to 2 f, 4 8 l6), etc. Experiment has shown that a system of such oscillators, however carefully tuned originally, will be subject to small variations which tend to disrupt the original and proper frequency relationship of the individual oscillators and will require frequent retuning. As the capacities and the resistances and also the operating voltages may be maintained constant with relative facility, this instability is presumably due to slight changes in the break-down and in the extinction voltage of the glow-discharge tubesa condition, which is difficult to remedy. I have now found that by deriving a fluctuating voltage from one of the oscillators and impressing such voltage upon the others, or at least on the next higher or lower frequency oscillator by means of an external electrode provides a simple and extremely efiective way of stabilizing the relative frequencies of said oscillators. An extremely effective way of carrying this concept into practice is to provide a series or system of glow-discharge tube oscillators having frequencies of f, 2), 4), 8f, etc., or in other words tuned in octaves. Each of these glow-discharge tubes is provided with an external electrode which is connected to a suitable point in the circuit of the next lower or the next higher oscillator. This point may be the common point of the glow-discharge tube and of the resistance connected in series therewith, as the voltage at this point varies very strongly during and in phase with the operation of the oscillator. I have found that a system of glow-discharge tube oscillators interlocked in this manner is so strongly stabilized that even intentional changes in the constants, (capacities or resistances), of some of the glow-discharge tube oscillators is without any effect on the frequency relationship once established. Although this interlocking arrangement directly and positively stabilizes only the relative frequencies of the oscillators, experiments have demonstrated that even the absolute pitch, that is the number of oscillations per second, remains extremely stable. Presumably, due to the extremely strong interlocking effect prevailing between the individual oscillators, the glow-discharge tubes in the system, some of which naturally tend to drift towards higher frequencies While other tubes tend to drift toward lower frequencies, mutually neutralize and counteract such drifting tendencies whereby a system of glow-discharge tube oscillators having positive relative frequency stability and an extremely high and heretofore unobtainable absolute frequency stability is obtained.

This interlocking connection between glowdischarge tube oscillators may be provided in various ways. Generally speaking, the stabilizing effect is the stronger, the closer are the two frequencies which are in a simple numerical relationship to each other. As in the tempered scale only the octaves are in a simple numerical relationship to each other, best results are obtained by tuning the oscillators to be interlocked in successive octaves and to provide the interlocking connection between adjoining octaves. This may be carried out by transferring stabilizing voltage from oscillator f to oscillator 2f, from oscillator 2f to oscillator 4], etc., in other words by stabilizing the higher octaves with oscillatory energy obtained from the next lower octave; or by stabilizing oscillator f with oscillations obtained from oscillator 2f, stabilizing oscillator 2] with oscillations obtained from oscillator 4f, etc., that is by stabilizing each oscillator by means of oscillations obtained from the next higher octave. In fact, it is possible to combine both systems and to impress on each oscillator stabilizing oscillations obtained from both the higher and the lower adjoining octave, in which case each oscillator except that of the lowest and of the highest frequency is provided with 2 external electrodes.

I, have found that it is advantageous to provide a series resistance of suitable value in the common branch of all interlocked glow-discharge tube oscillators, for example in series with the common source of current. This series resistance has a double eifect on the operation of the interlocked oscillators. First of all, the common resistance, if of proper value, acts as a coupling resistance between the several oscillators and provides an additional stabilizing effect, as this is disclosed in my U, S. Patent No. 2,017,542. At the same time it will be found that changing the value of this series resistance will collectively change the frequencies of the various oscillators without changing this frequency relationship which will remain at all times the same, such as, for example, an octave. Thus, the absolute frequency or pitch of a number of interlocked oscillators may be simultaneously adjusted by adjusting a single control knob. Of course, this circumstance is of considerable practical valuev in a practical electrical musical instrument.

Although the interlocking circuit of the invention provides a highly satisfactory stabilizing effect, in some cases, where extreme constancy of tuning is desired, it is advantageous to combine the stabilizing by means of an interlocked arrangement of the individual oscillators with the stabilizing by impressing a stabilizing voltage obtained from an external source of stablealternating current, such as, for example, a tuning fork oscillator, as this is disclosed in my U. S. Patent No. 2,044,360. This may be accomplished, for example, by providing a plurality of glow-discharge tube oscillators tuned to the frequencies f, 21, 4f, 81, I61, etc. Each of the glowdischarge tubes is provided with a pair of external electrodes, except the first or the last one, which have only a single external electrode. The frequency of oscillator 16 is impressed on oscillator 8f, that of 81 on the oscillator 47, that of the oscillator 4 on the oscillator 2f, etc., by means of one of the external electrodes on the respective tubes. The other external electrode of each tube is connected to each other and a suitable frequency obtained from a stable external source, for example from a tuning fork oscillator having the frequency of 4], is impressed on each glowdischarge tube. Thus, the stabilization of the relative frequencies of the oscillators is combined with the stabilization of the absolute frequencies whereby extreme stability is obtained.

In view of the fact that the described interlocking effect makes it necessary that all of the oscillators should oscillate at the same time, it is necessary to provide coupling means capable of selectively transferring oscillatory energy from the various oscillators to the common sound producing means, or to the common amplifier. This coupling may be of a capacitive, inductive or galvanic character, in other words it may be accomplished by means of condensers, transformers, resistances and combinations thereof, as it will be explained more fully hereinbelow.

Referring now more particularly to Fig. 1 of the drawing, in this figure the fundamental circuit embodying the invention is illustrated. Es-

sentially, two glow-discharge tube oscillators, O-l and O-2 are shown of which O-l comprises a glow-discharge tube Gl connected in series with a high resistance Pv-I, and a capacity C-l connected across the resistance, while O--2 comprises a glow-discharge tube G2 in series with a resistance R-Z, and a capacity C-2 connected across the resistance. Both oscillator O| and O2 are connected to the same source of direct current voltage B-l. As those skilled in the art know, oscillations will be produced both by oscillators O-l and O2, the frequency of said oscillations being substantially determined by the values of the capacity, resistance and the operating voltage of B-l. These constants are so selected that the frequencies of oscillators O--l and 0-2 are in a simple numerical relationship, preferably 1 to 2. This initial adjustment of the tuning of the oscillators, however carefully and accurately executed, will not remain permanent. In time, which according to the quality of the parts may be shorter or longer, the frequency of the individual oscillators will drift so that the original frequency relationship will be disturbed. The most important variable factors are the critical voltages, (break-down and extinction voltages), of the glow-discharge tubes which are subject to slight variations due to the variations of temperature, leakage, ageing, etc., and are difficult to control. To eliminate the disturbing effect of these difiicultly controllable variables, I provide an external electrode E2 on glow-discharge tube G2 and connect it to a point of oscillator O-l at which strong variations of potential occur during the production of oscillations. Such points of strongly variable potential may be found at various parts of the circuits. I have found, however, that excellent results are obtained by connecting external electrode E2 to the common point of glow-discharge tube GI and resistance R--l. It will be noted that during the production of oscillations by oscillator O--l, glow-discharge tube G--l will be alternately lighted and extinguished. In view of the fact that in the lighted or discharging condition of tube G-l, its internal resistance is very low, merely a few thousand ohms, while in the extinguished condition its resistance is extremely high, at least of the order of 10 or 20 megohms; in the first case, the potential of this common point will be very close to that of the upper or positive terminal of the battery, while in the latter case it will be considerably lower and closer to that of the lower or negative terminal of the battery. This strong fluctuation in' the value of the potential at this critical point is now impressed upon tube G--2 by means of the capacitive action of the external electrode and will exert an extremely strong stabilizing effect thereon. This stabilizing effect is so strong that the. relative frequencies of oscillators O-l and 0-4 will be positively maintained even in the case when C-l, Rl, or C2, R-2 are changed by a substantial amount. Therefore, any accidental changes in the values of these components or of the critical voltages of the tubes fail to disturb the constant and desired frequency relationship which will be permanently and positively maintained constant.

Although in Fig. 1 only 2 glow-discharge tube oscillators are shown, obviously any desired number of oscillators may be interlocked in the same way. Moreover, even though fixed resistances and condensers are illustrated in the drawing, the initial adjustments may be facilitated when one of these values is adjustable, as those skilled in the art will readily understand.

Fig. 2 depicts a modification of the fundamental inventive concept explained in connection with Fig. l. The circuit shown in Fig. 2 provides a double interlocking effect in that the individual glow-discharge tube oscillators are interlocked with more than one other glowdischarge tube oscillator.

The circuit shown in Fig. 2 includes 3 glowdischarge tube oscillators, O--3, 0-4 and O5. Oscillator O3 comprises a glow-discharge tube (3-3 with a series resistance R-3, and a condenser C3 across R-S; oscillator 0-4 comprises a glow-discharge tube G-4 with a series resistance R-4, and a condenser C-4 across 13-4; and oscillator -5 comprises a glow-discharge tube G- with a series resistanceR-J, and a condenser C-5 connected across resistance R--5. All of these glow-discharge tube oscillators are connected to the same source of direct current voltage B-2 and are consequently producing oscillations. The frequency of the oscillations of 0-3, O-4 and O5 is adjusted by proper selection or adjustment of the circuit constants to f, 2f and M, respectively. Stabilizing of the relative frequencies or" these oscillators is accomplished by providing an external electrode 13-4 on glow-discharge tube G--i and connecting it to the common terminal of tube G3 and of resistance R3 and by providing an external electrode E-5 on glow-discharge tube G5 and connecting it to the common terminal of tube (3-4 and resistance R4. This stabilizing effect, which in itself would be sufficient to maintain the proper frequency relationship of oscillators constant, is further assisted by providing an external electrode E-3 on tube G3 and connecting it to the common terminal of tube G4 and resistance R4, and by providing a second external electrode E- ifi on tube G-- l and connecting it to the common terminal of tube (Er-5 and resistance RFEV. I have found that this cross-stabilization generally provides even better results than the circuit shown in Fig. 1, although in most cases it is not necessary to carry the stabilization to such an extent.

Fig. 3 illustrates the stabilization of five glowdischarge tube oscillators in an electrical musical instrument, provision being made for the collective tuning or adjustment of the five oscillators. It will be noted that the circuit of Fig. 3 consists of 5 glow-discharge tube oscillators of conventional type. Oscillator 0-8 comprises tube G-B, resistance R6, and condenser 0-6; oscillator 0-? comprises tube G'l, resistance R-l', and condenser C-'l; oscillator 0-8 comprises tube G8, resistance R-8, and condenser Ci; oscillator O9 comprises tube G-B, resistance R9, and condenser C9; and oscillator Ol0 comprises tube Gl0, resistance R-lii, and condenser C-ID. In each of these oscillators the resistance is connected in series with the tube and the condenser is connected across the resistance. All of the oscillators are connected to a common source of direct current voltage B3 through a common adjustable resistance Pi having a value of, for example, 10,000 ohms. The physical constants of the various oscillators are so selected that the frequencies of the oscillations produced are in a simple numerical relationship with each other and preferably are tuned in octaves of a note of the tempered scale. Thus, if the frequency of the oscillator 0-5 is designated by f, the frequencies of the following oscillators are 2 4f, 8 and irif. Stabilization of this frequency relationship is accomplished by means of external electrodes E-l, E3, Ei and E-IO, provided on glow-discharge tubes G-l, G8, G9 and Gi0, respectively. External electrode E'! is connected to the common terminal of tube G6 and resistance RB; external electrode E8 is connected to the common terminal of tube G'i and resistance Rl; external electrode E-S is connected to the common terminal of tube G8 and resistance R8; and external electrode E-ifl is connected to the common terminal of tube G-9 and resistance R9 whereby a strong and permanently effective stabilizing effect is provided. It will be noted that adjustable resistance P-| is in the branch of the circuit which is common to all of the oscillators. Obviously, there will be a certain drop of voltage in resistance P-l in accordance with the adjustment thereof so that adjustment of resistance P-l will change the operating voltage of and thereby the frequency produced by the oscillators. However, due to the operation of the external electrodes, the frequency relationship of the individual oscillators will be maintained constant and merely the absolute frequency of the oscillations will be changed collectively. In other words, adjustment of resistance PI makes it possible to simultaneously tune all of the oscillators as a unit without disturbing the octave, (or other predetermined), frequency relationship. In addition to this valuable effect, resistance P-| provides a desirable coupling between the various oscillators and further enhances the stability thereof in accordance with the principles more fully explained in my U. S. Patent No. 2,017,542.

Of course, in a practical electrical in"*"cal instrument a much greater number of oscillators is required. Thus, in an electrical musical instrument having 7 octaves (disregarding the top note), 7 oscillators are required for each note of the tempered scale. To be more specific, 7 oscillators are provided tuned to successive octaves of the note C, 7 oscillators are provided tuned to successive octaves of the note C-t '7 scillators are provided tune to the successive octaves of the note D, and so forth, through the other notes of the tempered scale, De -T F, F#, G, Git, A, A#-.'', and B. Each of these 12 groups of oscillators are stabilized in the manner shown in Fig. 3, and each group is provided with a collective tuning device P-l. In this way the tuning of the '7 times 12; 84 oscillators is reduced to 12 adjustments what, of course, greatly facilitates the initial adjustment to the proper pitch and any future adjustments, should this become necessary at any time.

Fig. 4 illustrates a circuit including 5 stabilized or interlocked oscillators, provision being made for the selective transfer of the oscillatory energy from preselected oscillators to a common output circuit. Oscillator O-H comprises a glow-dis charge tube G-li. a resistance PFH and a condenser C-H; oscillator O-22 comprises a tube Gl2, a resistance Ri2 and a condenser C-i2; oscillator Oi3 comprises a tube G-i3, a resistance Ri3 and a condenser C-i 3; oscillator 0-44 comprises a tube Gl4, a resistance R-M and a condenser (3-H; and oscillator O| 5 comprises a tube Gl5, a resistance Ri 5 and a condenser C-l5. In each of these oscillators, the resistance is connected in series with the tube and the condenser is connected across the resistance, the values of the circuit constants being so adjusted that the frequencies produced by the various oscillators are in the ratio of f, 2f, 4 8 and I6 The free terminals of tubes G--l I, G-IZ, G--l3, G-M, and Gi5 are directly connected through a common adjustable series resistance P-2 to one of the terminals of source of direct current 13-4. A bleeder resistance X is provided for each oscillator for the purpose of providing a voltage drop which may be selectively transferred to a common output circuit, as it will be explained more fully hereinafter. Thus, bleeder resistance X-l is connected in series with resistance R-H in oscillator O-|l; resistance X-2 is connected in series with resistance R-IZ in oscillator -42; resistance X-3 is connected in series with resistance P..-l3; resistance 21-4 is connected in series with resistance RH; and resistance X- is connected in series with resistance Rl5. The lower terminals of all resistances X are connected to the other terminal of source of current 13-4 so that the circuit of all oscillators is completed and oscillations of predetermined frequencies will be produced. While the resistances R,l| to R-!5 are of the order of several megohms and are generally above 1 megohm, the bleeder resistances X are of a considerably lower value in order to prevent the introduction of high series impedances into the circuits of the individual oscillators what would tend to decrease the amplitude of the oscillations produced. I have found that good results are obtained by giving to the re sistances K values of a few thousand ohms, such as, for example, 5000 ohms. Of course, the resistances X do not have to have equal values for all of the oscillators. In fact, great advantages are obtained by adjusting the value thereof in reversed ratio to the original output of oscillatory energy by the various oscillators. As those skilled in the art know, generally greater capacities are needed in a glow-discharge tube oscillator for obtaining lower frequencies. On the other hand, the output of oscillatory energy is in part determined by the size of the capacity in the circuit and increases in direct proportion with the capacity. This tends to provide unduly great output for the lower notes and relatively weak output for the higher or highest notes in an electrical musical instrument of the described type. This difliculty can now be easily eliminated by providing bleeder resistances 'X of a relatively low value for the lowest oscillator 0-1 and increasingly higher values of X for the higher frequency oscillators. Togive a practical example, the resistances X may be increasing in the proportion of 1000, 2000, 3000, 4000, and 5000 ohms for the successive oscillators, although for best results this proportion is to be determined experimentally for each musical instrument as it obviously also depends on the ratio of capacity and resistance in each oscillator circuit. I

Stabilization of the frequency relationship between the various oscillators is provided by-means of external electrodes E-Jll, IL -l3, E-M and I i-"45 provided on tubes G-i2-, (Er-43, G-M and G-l5, respectively. External electrode E-l2 is connected to the common terminal of tube G-i i and resistance R.-i l-;- external electrode E-l3 is connected to the common terminal of tube G-l2 and resistance R- lZ; external electrode E-I4 is connected 'tothe common terminal of tube G-l3 and resistance Rl 3; and external electrode E-l5 is connected to the common terminal of tube G-l4 and resistance 3-44 whereby stabilization and the desired interlocking effect is obtained between the various oscillators. The object of variable resistance P--?. of about 10,000 ohms is the same as that of Pi in Fig. 3, to wit: to permit collective adjustment of the absolute pitch of the various oscillators and at the same time to increase the stabilizing effect for maintainingthe relative frequencies positively constant.

The selective transfer of oscillatory energy from the various oscillators to the common sound producing means is accomplished by meansof couv pling resistances Y. One end of each of these coupling resistances is connected to the common terminal of a resistance R and of a bleeder resistance X, while its other end is connected to a switching key S adapted to close a contact W upon actuation thereof. Thus, coupling resistance Y-l is connected between the common terminal of resistances R-ll and Xl, and switching key S-l; coupling resistance Y-2 is connected between the common terminal of resistances R-l2 and X-Z, and switching key S2; coupling resistance Y-3 is connected between the common terminal of resistances RI 3 and X3, and switching key S3; coupling resistance Y-A is connected between the common terminal of resistances RI4 and X4, and switching key S-4; and coupling resistance Y5 is connected between the common terminal of resistances Rl5 and X5, and switching key S'5. Contacts W-l to W-5 of switching keys S-lto 8-5, respectively, are all connected with each other by means of a common lead which in turn is connected through the primary winding of an output transformer T-l to the lower terminal of battery or source of direct current B4. Upon depression of any one of the switching keys S, an alternating current voltage is applied to the primary winding of the output transformer corresponding to the oscillator to which the switching key is connected. Simultaneous actuation of a plurality of switching keys will cause simultaneous transfer of oscillatory energy from the corresponding oscillators to the common primary winding. Preferably, the coupling resistances are of a relatively high value, such as'250,000 ohms each, in order to prevent tight coupling between the oscillators and the common output circuit which would cause detrimental reflection of energy from one oscillator to the others, keyed at the same time, and decrease of the, output when several keys are depressed at the same time. However, the value of the coupling resistance is by no means critical and may be varied within wide limits. The secondary winding of output transformer T-! is connected to a suitable low-frequency amplifier A-l which amplifies the electrical oscillations of musical frequency and introduces the amplified oscillations into a sound producing means L-l in conventional manner to convert the produced electrical oscillations into musical sounds. Of course, various additional or auxiliary devices, such as volume controls, tone controls and tremolo circuits may be associated with the amplifier. In view, of thefact that these devices are well-known to those skilled in the art and do not formpart of the present invention, no detailed description or-illustration thereof will be necessary.

- Fig. 5 illustrates a circuit of an electrical musical instrument which is much similar to the one shown in Fig. 4, with the difference, however,'that in addition to the stabilizing effect provided by interlocking the individual glow-discharge tube oscillators, also stabilizing by means of an external source of alternating current of constant frequency is provided. The circuit comprises 5 glow-discharge tube oscillators, 0-! 6 to O-20, each of said oscillators comprising a glow-discharge tube Gl 6 to G-20, respectively,

connected in series with a high resistance R-IB to R'-20, respectively, and a condenser 0-46 to 0 -20, respectively, connected across said resistance. Each of said oscillators is connected in series with a bleeder resistance X-6 to X-ID, respectively, and all of the oscillators are connected to a common source of direct current voltage B-E, an adjustable series resistance P-3 being connected in series with the source of current. Oscillators -16 to 0-20 are tuned to frequencies 2], 4 Bi, and IS respectively. The output of oscillators O-IB to 0-20 is selectively withdrawn through coupling resistances Y-6 to Y-ifl, respectively, connected between the common terminals of resistances R-I 6 to R-ZO and X-% to X-IB, respectively, and switching keys 5-8 to S-IU, respectively, cooperating with contacts W-S to W-IB, respectively. Same as in the circuit of Fig. 4, the primary winding of an output transformer T-2 is connected between the common lead of resistances X-G to X-IU and the common lead of contacts W-6 to W-l 0, the secondary winding of said transformer being connected to an amplifier A-2, the amplified oscillations being converted into sound by means of sound producing means L-2. Interlocking of the oscillators 0-16 to 0-20 is effected by means of external electrodes E-IE to E-IS, provided on glow-discharge tubes G-l 6 to G-l 9, respectively, said external electrodes being connected to the common terminal of tubes G-I'l to (3-20 and resistances R-ll to R-20, respectively. It will be noted that in this case the external electrode of each oscillator is interlocked with the next higher oscillator, rather than with the next lower oscillator, as is shown in Fig. 4, without any substantial difference in operation. In view of the fact that so far the circuit of Fig. 5 is practically identical with the one shown in Fig. 4, its operation will be readily understood by those skilled in the art without any further explanation.

Oscillators 0-l6 to 0-20 interlock in the described manner will positively maintain their frequency relationship for a practically unlimited length of time. To maintain also the absolute frequency of said oscillators constant, each of glow-discharge tubes 0-! 6, (3-! I, G-l 8, G-l 9, and G-20, is provided with a second external electrode E-Zl, E-22, E-23, E-24, and 13-25, respectively, all of which are connected together by means of a common lead. A source of alternating current of constant frequency, B, such as, for example, a tuning fork oscillator, is connected between the common lead of external electrodes E-Zl to E-25 and the common lead of glow-discharge tubes G-l6 to G-20. The frequency of this source of alternating current B is in a simple numerical relationship with those of oscillators 0-!6 to 0-20, best results being obtained when this frequency equals 4f. As it is disclosed in my Patent No. 2,044,360, in this case a strong stabilizing eifect is exerted on oscillators 0-!6 to 0-20. This stabilizing effect is the strongest on oscillator 0-! 8, the frequency of which equals that of B, it is somewhat less pronounced on oscillators 0-H and 0-! 9 and is weakest on oscillators 0-l6 and 0-29. However, this situation is completely compensated for by the interlocking effect provided in accordance with the principles of the present invention so that both the relative frequencies and the absolute frequencies of the oscillators will be positively maintained constant. Of course, a group of oscillators of the described character including a source of alternating current of stable frequency B has to be provided for each note of the tempered scale, in order to provide a complete electrical musical instrument, except that the output circuit including the output transformer, amplifier and sound producing means may be in common for all of these groups.

The external electrodes of the glow-discharge tubes are preferably provided in the form of a metal ring snugly fitting the glass vessel of the tubes, as this will appear from Figs. 6 and '7. Fig. 6 illustrates a glow-discharge tube of small dimensions comprising a glass vessel G-Zl having two internal electrodes, D-! and D2 provided therein. A small metal ring E-ZS is provided on the glass vessel in an encircling position and constitutes the external electrode exerting an electrostatic effect on the discharge between electrodes D-l and D-2.

Fig. 7 shows a similar glow-discharge tube having a glass vessel G-Zfl and two internal electrodes. Two ring-shaped external electrodes E-2'I and 13-28 are provided on vessel 6-22, each of which may exert an electrostatic effect on the discharge between internal electrodes D-3 and D-4, in accordance with its potential.

All of the circuits described in the foregoing include glow-discharge tube oscillators of the type in which a glow-discharge tube and a high resistance are connected in series and a condenser is connected across the resistance. Of course, the same results may be obtained in interlocking glow-discharge tube oscillators of the type in which the tube and resistance are likewise connected in series but the capacity is connected across the tube, rather than across the resistance. A circuit of this type is shown in Fig. 8. Although for the sake of simplicity only two glov -discharge tube oscillators, 0-23 and 0-24, are shown, of course, any desired number of glow-discharge tube oscillators may be interlocked in the same way. Oscillator 0-23 comprises a glow-discharge tube G-23 connected in series with a high resistance Pit-23, a condenser 0-23 being connected across the tube. Oscillator 0-24 comprises a glow-discharge tube connected in series with a resistance R-ZA and having a condenser 0-24 connected across the resistance. Oscillators 0-23 and 0-24 are connected to a common source of direct current voltage 3-6. The constants of oscillators 0-23 and 0-24 are so adjusted that their frequencies are in a simple numerical proportion, for example 1 to 2. Interlocking of the oscillators is accomplished by means of an external electrode E-29 which is connected to the common terminal of tube 6-23 and resistance 12-23. In view of the fact that the operation of this circuit is the same as that of the circuit shown in Fig. 1, it will be readily understood without any further description.

Fig. 9 illustrates a modification of the funda mental circuit shown in Fig. 1 in which the value of the alternating voltage transferred from the one oscillator to the other or others may be adjusted. The circuit, in which for the sake of simplicity only two glow-discharge tube oscillators are shown, essentially comprises a glowdischarge tube oscillator 0-25 consisting of a tube G-25 connected in series with a high resistance R-25, a condenser 0-25 of appropriate value being connected across the resistance. Oscillator 0-26 consists of a tube (3-25, connected in series with a high resistance R-ZB, a condenser 0-25 being connected across the resistance. Both oscillators 0-25 and 0-25 are connected to the same source of direct current voltage 13-! and are producing electrical oscillations in the conventional manner, the physical constants of the oscillators being so selected that the frequency of the oscillations is in a simple numerical relationship, such as, for example, 1 to 2. Stabilizing or interlocking of the oscillators is effected by means of an external electrode E3ll provided on tube G-26, so far this circuit being identical with the circuit shown in Fig. 1. Instead of, however, connecting the external electrode to the common terminal of tube (Fr-25 and resistance R-ZS, external electrode E-30 is connected to a sliding contact F adjustably arranged on high resistance R.-25. Thus, the alternating voltage and the stabilizing potential imparted to external electrode E-30 may be adjusted at will by ad justing the sliding contact F on the resistance and the desired stabilizing effectmay be maintained within preferred limits.

Although the present invention has been described in connection with a few preferred embodiments thereof, variations and modifications may be resorted to by those skilled in the art without departing from the principles of the present invention. Thus, instead of transferring stabilizing energy from one glow-discharge tube oscillator to only one or' two other glow-discharge tube oscillators, such stabilizing energy maybe transferred to any desired number of oscillators, provided their frequencies are in a simple numerical proportion with that of the stabilizing or master glow-discharge tube oscillator. This can be readily accomplished in View of the fact that the external electrodes are merely operated by electrostatic effect but they do not withdraw any appreciable amounts of energy from the circuit of the oscillator. I consider all of these variations and modifications to be within the true spirit and scope of the present invention.

I claim: I,

1. In a system for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationships, the combination comprising a plurality of at least three glow-discharge tube oscillators tuned to successive octaves of a note of the tempered scale, each of said oscillators including a tube having a resistance connected in series therewith and a condenser, means for supplying unidirectional potential to said oscillators to cause the production of electrical oscillations, an external electrode on each of said tubes, and means for connecting the external electrode of each of said tubes with the common terminal of tube and resistance in one of the other oscillators of adjoining frequency to interlock said oscillators with each other and to maintain their octave relationship constant. p

2. In a system for simultaneously producing a plurality of electrical oscillations of musical'frequency having constant frequency relationships, the combination comprising a plurality of glowdischarge tube oscillators, each of said oscillators including a tube havingpa resistance connected in series therewith and a condenser. means for supplying unidirectional current to said oscilla-- tors to cause the production of: electrical oscillations having simple numerical relations, a pair of external electrodes on each of said tubes, and means for connecting each of said external electrodes with the common terminal of tube and resistance in a different one of to interlock said oscillators with each other and to maintain their frequency relationship positively constant.

3. In a system for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationship the other oscillators the combination comprising a plurality of glowdischarge'tube oscillators tuned to successive octaves of a note of the tempered scale, each of said oscillators including a tube having a resistance connected in series therewith and a condenser, means for supplying unidirectional current to said oscillators to cause the production of electrical oscillations, a pair of external electrodes on each of said tubes with the exception of not more than two tubes having a single external electrode, and means for connecting said two external electrodes of each tube with the common terminal of tube and resistance in the oscillator of the next lower and next higher frequency respectively to interlock and to cross-stabilize said oscillators with each other and to maintain their frequency relationship positively constant.

4. In a system for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationships, the combination comprising a plurality of at least three glow-discharge tube oscillators tuned to successive octaves of a note of the tempered scale, each of said oscillators including a tube having a resistance connected in series therewith and a condenser, a source of direct current in common for said oscillators to supply unidirectional voltage thereto, an external electrode on each of said tubes, means for connecting each of said external electrodes with the common terminal of tube and resistance in the oscillator of nearest frequency to interlock said oscillators with each other and to maintain their relative frequency constant, and means for adjusting the unidirectional voltage acting on said oscillators to collectively change their absolute frequencies. 5. In a system for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationships, the combination comprising a plurality of at least three glow-discharge tube oscillators, each of said oscillators including a tube having a resistance connected in series therewith and a condenser,

a source of direct current in common for said oscillators to supply unidirectional voltage thereto and to cause the production of electrical oscillations having frequencies in simple numerical relations with each other, an external electrode each of said tubes connected to the common terminal of tube and resistance in one of the adjoining oscillators to interlock said oscillators with each other and to maintain their relative frequency constant, means including an adjustable resistance in series with said source of "direct currentfor collectively adjusting the absolute frequency'o'f said oscillators and to provide additional coupling between said oscillators.

6.'In an electrical musical instrument, the combination comprising a plurality of groups of "glow-discharge tube oscillators, each of said groups comprising a plurality of at least three glow-discharge tube oscillators tuned to success'ive octaves of the tempered scale and each of said oscillators including a tube having a resistance connected in series therewith and a condenser, a source of direct current in common for all of said oscillators, an external electrode on at least two of said tubes connected to the common terminal of tube and resistance in another one of the oscillators of the same group having the nearest frequency to interlock said oscillators with each other and to maintain their relative frequency constant, an adjustable series resistance for each of said groups in series with a part of the circuit in common with all of the oscillators of the group to collectively adjust the absolute frequency of said oscillators, and means for selectively withdrawing oscillatory energy from said oscillators.

7. In a system for simu taneously producing plurality of electrical oscillations having constant relative frequency, the combination comprising a plurality of at least three glow-discharge tube oscillators, each of said oscillators including a tube having a resistance connected in series therewith and a condenser, a source of direct current in common for said oscillators to apply unidirectional voltage thereto and to cause the production of electrical oscillations having harmonically related frequencies, an external electrode on at least two of said tubes connected to the common terminal of tube and resistance in one of the other oscillators having the nearest frequency to interlock said oscillator-s with each other and to maintain their relative frequency constant, and a second external electrode on each of said tubes connected to a source of alternating current of constant frequency to maintain the absolute frequency of said oscillators constant.

8. In a system for simultaneously producing a plurality of electrical oscillations having constant frequency, the combination comprising a plurality of at least three glow-discharge tube oscillators tuned to successive octaves of a note of the tempered scale, each of said oscillators including a tube having a resistance connected in series therewith and a condenser, a source of d rect current in common for said oscillators, an external electrode on each of said tubes connected to the common terminal of tube and resistance in one of the adjoining oscillators to interlock said oscillators with each other and to maintain their relative frequency constant, a source of alternating voltage having a constant frequency harmonically related to the frequency of said oscillators, a second external electrode on each of said tubes connected to said source of alternating voltage to maintain the absolute frequency of said oscillators constant, and means for selectively withdrawing oscillatory energy of stabilized frequency from said oscillators.

9. In an electrical musical instrument, the combination of a plurality of not less than three glow tube oscillators of harmonically related frequencies, and an external electrode on at least two of said tubes, each of said electrodes being connected to a point of oscillatory potential in an oscilla tor having the nearest frequency.

10. In a system for simultaneously producing a plurality of electrical oscillations having constant frequency relationships, the combination comprising a plurality of at least three glowdischarge tube oscillators, each of said oscillators including a tube and a resistance and a condenser of such value as to cause the production of harmonically related frequencies, a source of direct current for said oscillators, and at least one external electrode on at least two of said tubes. each of said external electrodes being connected to a point in the circuit of one of the other oscillators having the nearest frequency where the potential is variable thereby to stabilize the frequency relationship of said oscillators.

11. In asystem for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationships, the combination comprising a plurality of at least three glow-discharge tube oscillators,

each of said oscillators including a tube and a resistance and a condenser of such value as to cause the production of harmonically related frequencies, a source of direct current for said oscillators, an external electrode on at least two of said tubes, each of said external electrodes being connected to a point of varying alternating potential in the circuit of one of the other oscillators having the nearest frequency whereby the relative frequency of said oscillators is maintained constant, and means for selectively withdrawing oscillatory energy from said oscillators into a common load.

12. In a system for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationships, the combination comprising a plurality of at least three glow-discharge tube oscillators, each of said oscillators including a tube having a resistance connected in series therewith and a condenser connected across said resistance, means for supplying unidirectional current to said oscillators to cause the production of electrical oscillations having harmonically related frequencies, and an external electrode on at least two of said tubes, each of said external electrodes being connected to the common terminal of tube and resistance in one of the other oscillators having the nearest frequency.

13. In a system for simultaneously producing a plurality of electrical oscillations of musical frequency having constant frequency relationships, the combination comprising a plurality of at least three glow-discharge tube oscillators, each of said oscillators including a tube having a resistance connected in series therewith and a condenser connected across said tube, a source of direct current for said oscillators to cause the production of oscillations having harmonically related frequencies, and an external electrode on at least two of said tubes, each of said external electrodes being connected to the common terminal of tube and resistance in one of the other oscillators having the nearest frequency to interlock said oscillators with each other.

14. In a system for simultaneously producing a plurality of electrical oscillations having constant relative frequency, the combination comprising a plurality of glow-discharge tube oscillators, each of said oscillators including a tube having a resistance connected in series therewith and a condenser connected across the resistance, a source of direct current in common for said oscillators to cause the production of electrical oscillations having harmonically related frequencies, an external electrode on each of said tubes connected to the common terminal of tube and resistance in one of the adjoining oscillators to interlock said oscillators with each other and to maintain their relative frequency constant, and means including a bleeder resistance and a coupling resistance and a switching key for each of said oscillators to selectively withdraw oscillatory energy from said oscillators for a common output load, said bleeder resistance being connected in series with the high resistance of said oscillator thereby providing a point of oscillatory potential at the common point of said resistances, said coupling resistance being connected between said point of oscillatory potential and said switching key, and said output load being connected across all of said coupling resistance and switching keys whereby upon depression of said keys oscillatory energy will be transferred to said load from the corresponding oscillators.

15. In a system for simultaneously producing a plurality of electrical oscillations having constant relative frequency, the combination comprising a plurality of glow-discharge tube oscillators, each of said oscillators including a pair of serially connected elements comprising a tube and a resistance and a condenser connected across one of said elements, a source of direct current in common for said oscillators to cause the production of electrical oscillations having harmonically related frequencies, an external electrode on each of said tubes connected to the common terminal of tube and resistance in one of the adjoining oscillators to interlock said oscillators with each other and to maintain their relative frequency constant, and coupling means including a bleeder resistance and a coupling resistance and a switching key for each of said oscillators to selectively withdraw oscillatory energy from said oscillators for a common load,

said resistances having such values as to provide an extremely loose coupling between the individual oscillators and the common load and to prevent detrimental reflection of energy from one oscillator to the others through the common load, said bleeder resistance being connected in series with the high resistance of said oscillator thereby providing a point of oscillatory potential at the common point of said resistances, said coupling resistance being connected between said point of oscillatory potential and said switching key, and said output load being connected across all of said coupling resistances and switching keys whereby upon depression of said keys oscillatory energy will be transferred to said load from the corresponding oscillators.

16. In a system for simultaneously producing a plurality of electrical oscillations having constant relative frequency, the combination comprising a plurality of glow-discharge tube oscillators, each of said oscillators including a pair of serially connected elements comprising a tube and a resistance and a condenser connected across one of said elements, a source of direct current in common for said oscillators to cause the production of electrical oscillations having harmonically related frequencies an external electrode on each of said tubes connected to the common terminal of tube and resistance in one of the adjoining oscillators to interlock said 0scillators with each other and to maintain their relative frequency constant, a bleeder resistance for each oscillator having a value which is small with respect to that of the oscillator connected in series with the high resistance of the oscillator, and means including a coupling resistance and a switching key in series therewith connected to the common terminal of said oscillator and or said bieeder resistance for each of said oscillators to selectively withdraw oscillatory energy from said oscillators for a common output load connected across all of said coupling resistances and switching keys whereby upon depression of said keys oscillatory energy will be transferred to said load from the corresponding oscillators, said resistances having such values as to provide an extremely loose coupling between the individual oscillators and the common load and to compensate for variations in the output level of the various oscillators.

NICHOLAS LANGER. 

